1. Field of the Invention
The present invention relates to a motor in which a sleeve-type bearing impregnated with oil is used.
2. Description of the Related Art
As shown in FIG. 10, a conventional motor in which a sleeve-type bearing is used is constituted such that a sleeve2 impregnated with oil is fitted and fixed inside a cylindrical portion 1a of a housing 1 with a bottom and a shaft 3 is rotatably supported by the sleeve 2. The sleeve 2 is provided as a porous body made of a sintered metal impregnated with oil. A stator 4 is fitted and fixed to an outer peripheral face of the cylindrical portion 1a. A rotor 5 made of synthetic resin and injection-molded is integrally fixed to an upper end of the shaft 3. A magnet 7 is fixed inside the rotor 5 so as to be opposed to the stator 4 via a back iron 6 made of magnetic material. When electric current flows in the stator 4, rotational magnetic field is induced, so that the rotor 5 is rotated due to influence of magnetic interaction together with magnetic field of the magnet 7.
In the motor, lubrication oil oozed out of the sleeve 2 during rotation of the motor goes along a coupling portion 5a of the rotor 5 from an outer peripheral face of the shaft 3, and passes through a lower face of an inner side of the rotor 5 to leak outside the rotor through a clearance between the rotor 5 and an outer peripheral face of the back iron 6 (refer to arrow in FIG. 10).
As means for preventing such lubrication oil leakage, as shown in FIG. 11, a constitution that a lower end portion of the coupling portion 5a of the rotor 5 is received in an annular space defined by an inner peripheral face of the housing 1 and an upper end face of the sleeve 2, and an annular groove 9 is provided on an lower end face of the coupling portion 5a about the center axis of the shaft 3 has been known. With this constitution, since lubrication oil which has reached the coupling portion is captured in the annular groove 9, further advancing thereof is blocked. Such a technical idea has been disclosed in, for example, US2004/0052662A1 (FIG. 2) and U.S. Pat. No. 6,318,976B1.
In the means for preventing lubrication oil leakage, however, lubrication oil is temporarily captured in the annular groove 9, but the lubrication oil rides over a peripheral wall of the annular groove 9 on an outer diametrical side due to a time elapsing and such an action as a centrifugal force during rotation to reach an outer side peripheral face of the coupling portion 5a. As a result, the lubrication oil flows through an inner face of the rotor to leak outside of the rotor. Thus, the conventional motor has not been applied with sufficient means for preventing lubrication oil leakage.